Direct Liquid Injection Chemical Vapor Deposition of Molybdenum-Doped Bismuth Vanadate Photoelectrodes for Efficient Solar Water Splitting

Abstract

The direct liquid injection chemical vapor deposition (DLI-CVD) method is used to grow pristine and molybdenum (Mo)-doped monoclinic scheelite phase bismuth vanadate (BVO) photoelectrodes. Superior photoelectrochemical (PEC) performance is achieved with ∼200 ± 50 nm thick pristine and 8 at. % Mo-doped BVO films grown at 550 °C. Photocurrent densities as high as ∼1.65 and 3.25 mA/cm2 are obtained for pristine and optimum 8% Mo-doped BVO electrodes, respectively, at 1.23 V vs reversible hydrogen electrode (RHE) under visible light AM 1.5G (100 mW/cm2) in 0.5 M phosphate buffer electrolyte in the presence of 0.1 M Na2SO3 hole scavenger. Somewhat lower photocurrent densities of ∼1.5 and 2.4 mA/cm2 are obtained for pristine and optimum 8% Mo-doped BVO electrodes, respectively, in the absence of Na2SO3. Onset potential values as low as ∼0.1 and 0.3 V vs RHE are achieved with pristine and Mo-doped BVO films for sulfite and water oxidation, respectively. The increased photocurrent density with Mo doping is attributed to enhanced charge carrier density and film conductivity as confirmed by PEC and Mott–Schottky analyses. Because of the dense high quality polycrystalline structure, the DLI-CVD fabricated Mo-doped BVO electrodes exhibit substantial stability under water and sulfite oxidation conditions without any protective layer and/or oxygen evolution cocatalysts. Scanning electrochemical microscopy (SECM) studies confirm the low porosity of Mo:BVO films and production of oxygen in a local area of Mo:BVO electrode under light illumination.

Tuning Light‐Driven Water Splitting Efficiency of Mo‐Doped BiVO4: Optimised Preparation and Impact of Oxygen Evolution Electrocatalysts

“…RHE and at 420 nm showed an efficiency of 19 %, while the other samples do not exceed 13 %. Despite the IPCE values were obtained at about 400 mV lower bias potential, they were comparable with those obtained with other non‐structured Mo‐doped BiVO 4 samples reported in the literature under front‐side illumination (Table ) . In other words, the spray‐coated Mo : BiVO 4 photoanodes have a similar efficiency at a significant lower externally applied driving force.…”

“…In the last years, a wide range of incident photon‐to‐current efficiency (IPCE) values was published for Mo : BiVO 4 photoanodes prepared using a variety of different techniques . Moreover, in order to improve the efficiency, strategies such as a specific film architecture, doping and modification with OECs were applied.…”

High‐Temperature One‐Step Synthesis of Efficient Nanostructured Bismuth Vanadate Photoanodes for Water Oxidation

“…where C is the space charge capacitance of the semiconductor, e is the elementary charge value, ε the relative permittivity of the semiconductor (BiVO 4 , %68), [45] ε 0 is the permittivity in vacuum, E the applied potential, T is the temperature, and k is the Boltzmann constant. IPCE spectra were recorded at 1.23 V vs RHE in 1 m KB (pH 9.3) using a 100 W Xenon lamp equipped with an Oriel Cornerstone 130 1/8 monochromator and a motorized filter wheel (model, USFW-100, Newport) to block higher-order diffraction.…”

“…The carrier donor densities (N D ), obtained by the slopes in the linear rise domain, [44] were highest for the 12% porous film (%4.8 Â 10 19 cm À3 ) and lowest for the 80% one (%2.2 Â 10 18 cm À3 ), which are in line with those reported in the literature. [20,45] This could be attributed to the higher sintering temperature, resulting in fewer densities of boundaries from the 12% porous films, compared with 46% and 80% porous ones. The electrochemical impedance spectra (EIS) of these three photoanode morphologies further confirm the above suggestions (Figure 5c).…”

Direct Liquid Injection Chemical Vapor Deposition

“…Kemstream ® 's injector (Figure 7a) can be found on Annealsys ® CVD and ALD machines and process are called "direct liquid injection (DLI)-CVD and ALD" [94][95][96]. The Brooks ® DLI Vaporizer Systems (Figure 7b) were successfully implemented in industrial CVD [97][98][99] and ALD [34,[100][101][102][103][104][105] processes, as well. The major part of the DLI-CVD industry is dedicated to the deposition of very well known III-V semiconductors, in which HORIBASTEC Liquid Vaporization Systems (Figure 7c) are broadly used [106].…”